Mixed state in high temperature superconductors

Abstract

In high T c superconductors the macroscopic mixed state (MACMS), corresponding to a mixture of macroscopic large supeconducting and normal domains, may be realized in magnetic field H. On the H-T phase diagram MACMS lies between high temperature normal state and low temperature Abrikosov vortex state. The irreversibility line corresponds in this case to the topological cross-over from MACMS with isolated singly-connected superconducting “droplets”, surrounded by the normal phase, to be sponge-like MACMS with multiply-connected superconducting “body”, surrounding isolated normal-state domains, which finally decay into Abrikosov vortices, as temperature goes down. The irreversibility appears due to the change of connectivity caused by the transition from superconducting droplets to superconducting sponge. The possibility of the multiple ф 0 normal cores existence has been demonstrated. Related experimental data on resistivity, magnetization, critical currents of high T c superconductors in magnetic field are discussed. The new experiments have been proposed to check predictions of the MACMS model.